Commercial aircraft usually comprise wing-mounted engines. For civil use turbofan engines with a high bypass ratio are preferred as they provide a low thrust specific fuel consumption, wherein by enlarging the diameter of a fan section, the bypass ratio of a turbofan engine can be increased. Hence, on one hand, for better fuel efficiency the radial extension of turbofan engines is to be increased and on the other hand the preferred mounting position under a wing strongly limits the maximum possible diameter of an engine as the length of the landing gear may not exceed a certain length due to weight restrictions, the possible shock absorption characteristics and resizing effects of the main landing gear on the overall configuration of the aircraft. Consequently, for some configuration the engine will be mounted closely to the wing.
A support structure is usually employed for mounting an engine to a wing, which support structure is faired by a pylon extending from an engine nacelle to the underside of the wing near its leading edge. Along the leading edge commercial aircraft usually comprise an arrangement of extendable high lift devices, e.g. one or more of a variety of different possible leading edge high lift devices comprising slats, Krueger devices, droop nose devices etc., that allow an increase especially of the maximum lift in low speed flight regimes generated by the wing. In a leading edge region that is close to the pylon of the support structure the extension of a high lift surface element is geometrically spanwise limited, due to the sweep angle of the wing and the vertical distance between the leading edge high lift device and a nacelle or engine cowling. Therefore, a slat arrangement is interrupted such that a collision with the pylon and the engine are avoided. In order to at least partially recover the aerodynamic penalty due to this interruption, there are different solutions known in the state of the art.
One solution is directed to a Krüger flap which is installed e.g. in the area inboard of the engine pylon. The advantage of the Krüger flap is that a smaller deployment room is needed compared to that of a conventional slat. However, even though its deployment room is small, for extremely closely coupled engines it might still be too large. Another disadvantage is that it relies on a complex kinematic system that requires frequent maintenance.
Another known solution is to introduce strakes as passive devices, which strakes create a trailing vortex that delays the stall in the region of the slat interruption. The strake vortices are created in the time when the overall aircraft exceeds a certain angle of attack. Nevertheless, as the strakes are usually fixed, they create unwanted drag before this angle of attack is reached.
EP 2 167 380 A1 discloses a nacelle of a wing mounted engine comprising several fin-shaped vortex generators on one side of the nacelle for improving the maximum lift.